Safety fault interrupter circuit with power fault monitor

ABSTRACT

An apparatus includes a safety fault interrupter circuit. The safety fault interrupter circuit includes a safety fault monitor coupled to a first bias node and configured to selectively assert a fault interrupter signal based at least in part on a first bias voltage and a first power consumption. The safety fault interrupter circuit also includes a power fault monitor for the safety fault monitor, wherein the power fault monitor is coupled to a second bias node and is configured to selectively assert the fault interrupter signal based at least in part on a second bias voltage and a second power consumption that is less than the first power consumption.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/662,451, filed Apr. 25, 2018, which is hereby incorporated byreference.

BACKGROUND

Power supplies and power converters are used in a variety of electronicsystems. Electrical power is generally transmitted over long distancesas an alternating current (AC) signal. The AC signal is divided andmetered as desired for each business or home location, and is oftenconverted to direct current (DC) for use with individual electronicdevices or components. Modern electronic systems often employ devices orcomponents designed to operate using different AC or DC voltages.

There are ongoing safety issues related to the electrical grid and faultscenarios that arise due to component failure and/or human error. Toaccount for such scenarios, ongoing standardization and safetyorganizations have developed safety fault interrupter specifications.One example specification is UL943, which defines the requirements for aground fault circuit interrupter (GFCI). Another example specificationdefines the requirements for an arc fault circuit interrupter (AFCI).Such specifications are updated over time as needed, and efforts toprovide reliable and cost-effective circuits in compliance with suchspecifications are ongoing.

One issue that has been identified for some safety fault interruptercircuits is that providing an integrated circuit (IC) bias voltagesafely over all conditions requires 2 or 4 large high power shuntresistors to ensure a reliable design, which will continue to operateproperly over all UL test conditions. For example, UL943 states thateach component “shall be tested by imposing a fault on the componentwhich simulates the typical failure mode for the component”. Thus, avoltage dropping resistor must withstand a single open circuit. Also,existing fault detection IC's do not provide a mechanism to detect anexternal AC-DC circuit fault to ensure de-energization as required byUL943. Efforts to improve safety fault interrupters are ongoing.

SUMMARY

In accordance with at least one example of the disclosure, an apparatuscomprises a safety fault interrupter circuit. The safety faultinterrupter circuit comprises a safety fault monitor coupled to a firstbias node and configured to selectively assert a fault interruptersignal based at least in part on the first bias voltage and a firstpower consumption. The safety fault interrupter circuit also comprises apower fault monitor for the safety fault monitor. The power faultmonitor is coupled to a second bias node and is configured toselectively assert the fault interrupter signal based at least in parton the second bias voltage and a second power consumption that is lessthan the first power consumption.

In accordance with at least one example of the disclosure, a safetyfault interrupter integrated circuit (IC) comprises a safety faultmonitor circuit configured to selectively assert a fault interruptersignal. The safety fault interrupter IC also comprises a power faultmonitor circuit for the safety fault monitor circuit, wherein the powerfault monitor circuit is configured to selectively assert the faultinterrupter signal. The power fault monitor circuit comprises a voltagesense circuit configured to compare a first voltage input to the safetyfault monitor circuit and a second voltage input to the power faultmonitor circuit, and to determine a comparison result. The power faultmonitor circuit also comprises a switch operated based on the comparisonresult.

In accordance with at least one example of the disclosure, an ICcomprises a first node configured to receive a first voltage. The ICalso comprises a second node configured to receive a second voltage. TheIC also comprises a safety fault monitor circuit configured toselectively assert a fault interrupter signal based at least in part ona first voltage, wherein the safety fault monitor circuit has a firstpower consumption. The IC also comprises a power fault monitor circuitfor the safety fault monitor circuit. The power fault monitor circuit isconfigured to selectively assert the fault interrupter signal based atleast in part on a comparison of the first voltage and the secondvoltage, wherein the power fault monitor circuit has a second powerconsumption that is less than the first power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various examples, reference will now bemade to the accompanying drawings in which:

FIG. 1 shows a block diagram of a system with a safety fault interruptercircuit in accordance with various examples;

FIG. 2 shows a schematic diagram of a system with a safety faultinterrupter circuit in accordance with various examples;

FIG. 3 shows another schematic diagram of a system with a safety faultinterrupter circuit in accordance with various examples;

FIG. 4 shows a schematic diagram of a safety fault monitoring scenario,where various internal components of a safety fault interrupter circuitare represented in accordance with various examples; and

FIGS. 5A and 5B show schematic diagrams of safety fault monitoringscenarios, where various internal components of a safety faultinterrupter circuit are represented in accordance with various examples.

DETAILED DESCRIPTION

Disclosed herein are safety fault interrupter circuits having a safetyfault monitor and a power fault monitor for the safety fault monitor.Example safety fault monitors are configured to detect ground faults orarc faults. In either case, each of the safety fault monitor and thepower fault monitor is able to assert the same fault interrupter signal.Without limitation, in some examples, the disclosed safety faultinterrupter circuits are manufactured as monolithic integrated circuits(ICs) or as multi-die modules. In at least some examples, the safetyfault monitor and the power fault monitor of a safety fault interruptercircuit are designed for use with different bias voltages and/or havedifferent power consumptions. As used herein, “a bias voltage” is adirect current (DC) voltage (e.g., derived from an AC power line) thatenables proper operation of a circuit or sub-circuit.

An example safety fault interrupter circuit includes a safety faultmonitor configured to selectively assert a fault interrupter signalbased at least in part on a first bias voltage and a first powerconsumption. As an example, the safety fault monitor uses the first biasvoltage at least to power sensing and switching operations with thefirst power consumption, where the safety fault monitor acts in responseto a fault trigger (e.g., ground fault trigger or arc fault trigger). Asan example, in a ground fault circuit interrupter (GFCI) scenario, afault trigger occurs when an unequal opposite current of defined maximumamplitude is sensed across the hot (Live) to neutral (return) wires ofan AC power line, where the fault is indicative of a possible humanelectrocution from hot to earth ground. As another example, in an arcfault circuit interrupter (AFCI) scenario, a fault trigger occurs whencurrent and voltage sense signals along a cable are determined to havean arc signature. Regardless of the type of safety fault to be detected,the first bias voltage is used to power internal IC circuitry including,but not limited to, any combination of sensing circuits, signalconditioning circuits, monitoring circuits, and/or power deactivationcircuits.

An example safety fault interrupter circuit also includes a power faultmonitor for the safety fault monitor, where the power fault monitor isconfigured to selectively assert the fault interrupter signal based atleast in part on a second bias voltage and a second power consumptionthat is less than the first power consumption. As an example, the powerfault monitor uses the second bias voltage at least to power switchingoperations in response to one or more power fault triggers. In someexamples, the power fault trigger circuit is a simple and low powercircuit compared to the safety fault monitor.

In some examples, the second bias voltage has a no power-fault magnitudethat is less than a no power-fault magnitude of the first bias voltagelevel. As used herein, “no power-fault magnitude” refers to a voltagelevel during a normal monitoring state of the safety fault interruptercircuit (before a power loss fault occurs). In other examples, the nopower-fault magnitude of the first bias voltage level is the same or isless than the second bias voltage level. Regardless of the particular nopower-fault magnitudes for the first and second bias voltage levels,under normal power loss conditions, the first bias voltage level isexpected to drop faster than the second bias voltage level in the eventof a power loss fault. In a converse example, under normal energizingconditions, the second bias voltage is expected to rise faster than thefirst bias level. In different examples, there are different types offaults that the safety fault interrupter circuit is able to respond to.In some examples, the safety fault monitor asserts the fault interruptersignal in response to a ground fault condition. In other examples, thesafety fault monitor asserts the fault interrupter signal in response toan arc fault condition. Meanwhile, the power fault monitor asserts thefault interrupter signal in response a fault in the power supplyproviding the first bias voltage. Such power faults are detected, insome examples, by comparing the magnitudes of the first and second biasvoltages.

In some examples, the power fault monitor includes a voltage sensecircuit configured to compare the first bias voltage input to the safetyfault monitor with the second bias voltage input to the power faultmonitor. Based on the comparison results, the power fault monitorasserts the fault interrupter signal. In some examples, the power faultmonitor asserts the fault interrupter signal when the comparison resultindicates that a drop rate of the first bias voltage relative to a droprate of the second bias voltage exceeds a threshold. In some examples,the power fault monitor asserts the fault interrupter signal when thecomparison result indicates that the difference between the first andsecond bias voltages is more than a threshold amount. To provide abetter understanding, various safety fault interrupter circuit options,fault monitor options, and fault response options are described usingthe figures as follows.

FIG. 1 shows a block diagram of a system 100 with a safety faultinterrupter circuit 102 in accordance with various examples. In someexamples, the safety fault interrupter circuit 102 is an IC compatiblewith GFCI, AFCI, and/or other fault standards. As shown, the system 100comprises the safety fault interrupter circuit 102, which is coupled toa first power converter 114 configured to provide a first bias voltage(BIAS_1) at node 118 of the safety fault interrupter circuit 102. Insome examples, the first power converter 114 comprises at least onediode, a resistor, and a capacitor arranged to rectify and convert aninput voltage available at node 122 to BIAS_1. In other examples, thefirst power converter 114 comprises a switched-mode power supply (SMPS)configured to convert an input voltage available at node 122 to BIAS_1.

As shown in FIG. 1, the system 100 also comprises a second powerconverter 116 configured to provide a second bias voltage (BIAS_2) atnode 120 of the safety fault interrupter circuit 102. In some examples,the second power converter 116 comprises at least one diode, a resistor,and a capacitor to provide BIAS_2 at node 120 of the safety faultinterrupter circuit 102. In different examples, the no power-faultmagnitudes for BIAS_1 and BIAS_2 vary depending on the respectivecircuits used with the safety fault monitor 112 and the power faultmonitor 104. In different examples, the no power-fault magnitude forBIAS_1 is greater than, equal to, or less than the no power-fault valuefor BIAS_2 (e.g., the no power-fault values for BIAS_1 and BIAS_2 arebetween 5-20 Volts, where BIAS_1 and BIAS_2 are selected depending on aspecific IC implementation).

In some examples, the second power converter 116 and the first powerconverter 114 share one or more diodes. Also, in some examples, aresistor value for the second power converter 116 is higher than aresistor value for the first power converter 114 (e.g., 20-30 timeshigher). In one example, a resistor value for the second power converter116 is 750 kΩ while a resistor value for the first power converter 114is 27 kΩ. Also, in some examples, a capacitor value for the second powerconverter 116 is equal to or less than a capacitor value for the firstpower converter 114.

In operation, the safety fault interrupter circuit 102 detects andresponds to faults using a safety fault monitor 112 and a power faultmonitor 104. In at least some examples, the safety fault monitor 112selectively asserts a fault interrupter signal to node 130 of the safetyfault interrupter circuit 102 based on one or more triggers, whereBIAS_1 is at least used to power switching operations of the safetyfault monitor 112 (to assert the fault interrupter signal). In differentexamples, different triggers for the safety fault monitor 112 are basedon one or more signals 122 received at input nodes 124 of the safetyfault interrupter circuit 102. Also, as desired, the safety faultinterrupter circuit 102 provides one or more input/output signals122/126 via input/output nodes 124/128. In an example GFCI scenario, thesafety fault monitor 112 senses differential current to and from an ACload. In an example AFCI scenario, the safety fault monitor 112 senses acurrent/voltage arc signature along a cable coupled to an AC load.

Meanwhile, the power fault monitor 104 selectively asserts the faultinterrupter signal to node 130 of the safety fault interrupter circuit102 based on one or more other triggers, where BIAS_2 is at least usedto power switching operations of the power fault monitor 104 (to assertthe fault interrupter signal). In at least some examples, the powerfault monitor 104 detects and responds to a BIAS_1 power converter faultbased on a comparison of BIAS_1 and BIAS_2, where the comparison resultsis used as a trigger to assert the fault interrupter signal. In oneexample, the power fault monitor 104 asserts the fault interruptersignal when the comparison result indicates that a drop rate of BIAS_1relative to a drop rate of BIAS_2 voltage exceeds a threshold. Inanother example, the power fault monitor 104 asserts the faultinterrupter signal when the comparison result indicates that BIAS_1varies from or is less than BIAS_2 by more than a threshold amount. Inany of these test conditions the input voltage 122 may be conditioned(rectified and/or reduced) and optionally used as an additionaltrigger/threshold level for the comparison of BIAS_1 and/or BIAS_2.

As an example fault, if power is lost at node 122, the value of BIAS_1at node 118 will drop below a predetermined voltage threshold within apredetermined time (on the order of milliseconds) before the value ofBIAS_2 at node 120 is affected by the power loss at node 122. If a faultcondition is determined to exist within power converter 114 or elsewhererelated to a failure of the IC's primary fault monitor 112 or anyassociated external circuitry, this delayed loss of power at the powerfault monitor 104 enables assertion of the fault interrupter signal atnode 130 even if the majority of the IC circuitry corresponding to thesafety fault interrupter circuit 102 (including the safety fault monitor112) has already been de-energized. In some examples, the power faultmonitor 104 and the second power converter 116 employs components thatare small and efficient such that BIAS_2 is stored longer than BIAS_1 inresponse to a power loss fault within or associated with power converter114. Thus, in one example, the power fault monitor 104 asserts the faultinterrupter signal when a comparison result indicates that a drop rateof BIAS_1 relative to a drop rate of BIAS_2 voltage exceeds a threshold.In another example, the power fault monitor 104 asserts the faultinterrupter signal when a comparison result indicates that BIAS_1 variesfrom or is less than BIAS_2 by more than a threshold amount. In at leastsome examples, the input voltage at node 122 is used as a qualifier ortrigger during the fault determination process.

In some examples, the power fault monitor 104 is designed with asufficiently low power consumption and with storage elements (e.g.,capacitors) within or after the second power converter 116, such thatthe power fault monitor 104 is sufficiently powered to trigger the faultinterrupter signal in response to a power loss fault. In one example,the extended “hold-up” power provided through a switch 108 of the powerfault monitor 104 lasts on the order of 5 milliseconds after the actualloss of power at node 122, or from a power loss at BIAS_1 occurring asan example by a fault within power converter 114 and/or associatedinternal or external circuitry.

To perform the comparison of BIAS_1 and BIAS_2 (and optionally the inputvoltage at node 122), the power fault monitor 104 employs a voltagesense circuit 110. In some examples, the voltage sense circuit 110comprises one or more resistors, comparators, op-amps, voltagereferences, gates, flip-flops, and/or other circuit componentsconfigured to compare the two bias voltage signals and optionally theinput voltage at node 122. In some examples, RC timing elements are usedto perform the comparison. To perform switching operations, the powerfault monitor 104 monitors voltage thresholds to detect a power faultand/or power converter fault. As shown, the power fault monitor 104comprises a driver circuit 106 powered by BIAS_2, where the drivercircuit 106 directs the switch 108 to close in response to a comparisonresult from the voltage sense circuit 110 that is associated with afault trigger. In some examples, the switch 108 is a transistor having acontrol terminal, a first current terminal, and second current terminal.In this example, the driver circuit 106 provides a control signal to thecontrol terminal of the transistor in response to a comparison resultfrom the voltage sense circuit 110 that is associated with a faulttrigger.

In some examples, the fault interrupter signal is asserted by the powerfault monitor 104 in response to a fault within the power converter 114and/or associated circuitry. In one example, the fault interruptersignal 130 triggers a silicon-controlled rectifier (SCR) signal thatcauses latching contacts of an external circuit to open.

FIG. 2 shows a schematic diagram of a system 200 with a safety faultinterrupter circuit 102A in accordance with various examples. In FIG. 2,the safety fault interrupter circuit 102A is an example of the safetyfault interrupter circuit 102 of FIG. 1 in a GFCI scenario (the safetyfault monitor 112A detects ground faults). As shown, the system 200shows a power line 202 with “hot” and “neutral” wires. In at least someexamples, a metal-oxide varistor (MOV) 206 is coupled between the wiresof the power line 202 to provide over-voltage protection. The power line202 provides power to a load 210 via latching contacts 212.

In FIG. 2, the safety fault interrupter circuit 102A receives sensesignals, V_FB and V_REF, from the power line 202 via a sense transformer204, where a capacitor (C1) is positioned between the sense transformer204 and a V_FB node of the safety fault interrupter circuit 102A. In theexample of FIG. 2, the winding ratio of the sense transformer 204 is1000:1 (i.e., the sense transformer 204 includes a core with 1000windings of wire 218 around the core). In other examples, the windingratio varies to provide a sense signal to the safety fault interruptercircuit 102A via the wire 218. In operation, the safety faultinterrupter circuit 102A detects and responds to faults by asserting afault interrupter signal 130A (e.g., an SCR signal) that causes, forexample, a solenoid 214 to open the latching contacts 212. Examplefaults include real faults, simulated faults, self-test ground faults(using the test button 208), real grounded neutral faults, and simulatedgrounded neutral faults.

As an example, when a sufficient current imbalance in the wires of thepower line 202, a net current flows through the sense transformer 202,causing a magnetic flux to be created. This magnetic flux results inelectrical current being induced on the wire 218, which is wound aroundthe sense transformer 204 and is coupled to the V-REF and V_FB nodes ofthe safety fault interrupter circuit 102A. The induced current on thewire 218 causes a voltage difference at the V-REF and V_FB nodes. Whenthe voltage difference exceeds a predetermined threshold value, thesafety fault interrupter circuit 102A asserts a fault interrupter signal130A (e.g., a SCR signal in FIG. 2) that causes the latching contacts212 to be opened. In at least some examples, the above-noted faultdetection and response scenario is performed by a safety fault monitor112A (an example of the safety fault monitor 112 in FIG. 1) of thesafety fault interrupter circuit 102A, where a first bias voltage (e.g.,BIAS_1) is used by the safety fault monitor 112A at least for voltagedifference sensing between V_FB and V_REF and for switching operationsto assert the fault interrupter signal 130A in response to a trigger. Inthe example of FIG. 2, BIAS_1 is provided to the safety faultinterrupter circuit 102A via a bridge 216, a capacitor (C2), and aresistor (R_DROP1), where these components correspond to a powerconverter (e.g., the first power converter 114 in FIG. 1).

As represented in FIG. 2, the safety fault interrupter circuit 102A alsoreceives a second bias voltage (e.g., BIAS_2) and includes a power faultmonitor 104A (an example of the power fault monitor 104 in FIG. 1). Insome examples, the safety fault monitor 112A is a ground fault monitor,while the power fault monitor 104A performs primary or BIAS_1 power lossmonitoring. In such examples, BIAS_2 is used to power an internaldedicated circuit as well as to monitor and detect an input voltagefault condition on BIAS_1. In the example of FIG. 2, BIAS_2 is providedto the safety fault interrupter circuit 102A via the bridge 216, aresistor (R_AUX1), and a capacitor (C3), where these componentscorrespond to a power converter (e.g., the second power converter 116 inFIG. 1).

In at least some examples, the power fault monitor 104A asserts a faultinterrupter signal 130A (e.g., a SCR signal) that causes the latchingcontacts 212 to be opened, where BIAS_2 is used by the power faultmonitor 104A at least for switching operations to assert the faultinterrupter signal 130A in response to a trigger (e.g., a primary inputor BIAS_1 power fault condition). In some examples, the power faultmonitor 104A uses a comparison result of BIAS_1 and BIAS_2 as a triggerto indicate an imminent primary power fault condition and, in response,to assert the fault interrupter signal 130A. In one example, the powerfault monitor 104A asserts the fault interrupter signal 130A when thecomparison result indicates that a drop rate of BIAS_1 relative to adrop rate of BIAS_2 voltage exceeds a threshold. In another example, thepower fault monitor 104A asserts the fault interrupter signal 130A whenthe comparison result indicates that the difference between BIAS_1 andBIAS_2 is greater than a threshold amount.

FIG. 3 shows another schematic diagram of a system 300 with a safetyfault interrupter circuit 102B in accordance with various examples. InFIG. 3, the safety fault interrupter circuit 102B is an example of thesafety fault interrupter circuit 102 of FIG. 1, or the safety faultinterrupter circuit 102A of FIG. 2 in another GFCI scenario (the safetyfault monitor 112B detects ground faults). As shown, the system 300shows a power line 302 with “hot” and “neutral” wires. In at least someexamples, a varistor 308 is coupled between the wires of the power line302 to provide over-voltage protection. The power line 302 providespower to a load 310 via latching contacts 312.

In FIG. 3, the safety fault interrupter circuit 102B receives sensesignals, V_FB and V_REF, from the power line 302 via a first sensetransformer 306, where a voltage divider (formed using resistors, R3 andR4) is positioned between the first sense transformer 306 and a V_FBnode of the safety fault interrupter circuit 102B. In the example ofFIG. 3, the winding ratio of the first sense transformer 306 is 1000:1(i.e., the sense transformer 306 includes a core with 1000 windingsaround the core using a wire 318). In other examples, the winding ratiovaries to provide a sense signal to the safety fault interrupter circuit102B via the wire 318. In operation, the safety fault interruptercircuit 102B detects and responds to faults by asserting a faultinterrupter signal 130B (e.g., an SCR signal) that causes a solenoid 316to open the latching contacts 312. Example faults include real faults,simulated faults, self-test ground faults, real grounded neutral faults,and simulated grounded neutral faults.

As an example, when a sufficient current imbalance in the wires of thepower line 302, a net current flows through the first sense transformer306, causing a magnetic flux to be created. This magnetic flux resultsin electrical current being induced on a wire 318, which is wound aroundthe first sense transformer 306 and is coupled to the V-REF and V_FBnodes of the safety fault interrupter circuit 102B. The induced currenton the wire 218 causes a voltage difference at the V-REF and V_FB nodes.When the voltage difference exceeds a predetermined threshold value, thesafety fault interrupter circuit 102B asserts a fault interrupter signal130B (e.g., a SCR signal in FIG. 2) that causes the latching contacts312 to be opened.

In at least some examples, the above-noted fault detection and responsescenario is performed by a safety fault monitor 112B (an example of thesafety fault monitor 112 in FIG. 1, or the safety fault monitor 112A inFIG. 2) of the safety fault interrupter circuit 102B, where a first biasvoltage (e.g., BIAS_1) is used by the safety fault monitor 112B at leastfor switching operations to assert the fault interrupter signal inresponse to a trigger. The example system 300 of FIG. 3 is similar tothe example system 200 of FIG. 2. For the system 300, a second sensetransformer 304 is included to enable identification of mis-wireconditions, which could lead to lack of proper protection by the safetyfault interrupter circuit 102B. In the example of FIG. 3, the windingratio of the second sense transformer 304 is 200:1 (i.e., the sensetransformer 304 includes a core with 200 windings around the core usinga wire 320). In other examples, the winding ratio varies to provide asense signal to the safety fault interrupter circuit 102B via the wire320.

The windings formed by the wire 318 have a function similar to thewindings formed by the wire 218 described in FIG. 2 (the windings inducea current in the wire 318 proportional to the current along the powerline 302), where V_FB is compared to V_REF to identify an induced energyas would occur when a hazardous external current path takes placebetween Hot and Earth Ground. For the system 300, BIAS_1 is provided tothe safety fault interrupter circuit 102B via diodes D1 and D2, aresistor (R_DROP2), and a capacitor (C4), where these componentscorrespond to a power converter (e.g., the first power converter 114 inFIG. 1). In the example of FIG. 3, the second sense transformer 304 isused to identify mis-wiring where NG_OUT and GND are used to induce asignal onto Hot/Neutral wires 302, where a wiring error is identifiedbased on an improper signal coupled back into the first sensetransformer 306 and into V_FB respectively. PH and FT in concert with Q2are used to for self-testing of the protection circuits.

As represented in FIG. 3, the safety fault interrupter circuit 102B alsoreceives a second bias voltage (e.g., BIAS_2) and includes a power faultmonitor 104B (an example of the power fault monitor 104 in FIG. 1, orthe power fault monitor 104A in FIG. 2). In the example of FIG. 3,BIAS_2 is provided to the safety fault interrupter circuit 102B via D1and D2, a resistor (R_AUX2), and a capacitor (C5), where thesecomponents correspond to a power converter (e.g., the second powerconverter 116 in FIG. 1).

In at least some examples, the power fault monitor 104B asserts a faultinterrupter signal 130B (e.g., a SCR signal) that causes the latchingcontacts 312 to be opened. In some examples, BIAS_2 is used by the powerfault monitor 104B to identify a power fault condition (e.g., a primaryor BIAS_1 power fault), and to perform switching operations to assertthe fault interrupter signal 130B in response to the fault conditionwithin the circuitry servicing BIAS_1. In some examples, the power faultmonitor 104B uses a comparison result of BIAS_1 and BIAS_2 as a triggerto assert the fault interrupter signals. In one example, the power faultmonitor 104B asserts the fault interrupter signal 130B when thecomparison result indicates that a drop rate of BIAS_1 relative to adrop rate of BIAS_2 voltage exceeds a threshold. In another example, thepower fault monitor 104B asserts the fault interrupter signal 130B whenthe comparison result indicates that the difference between BIAS_1 andBIAS_2 is greater than a threshold amount.

Also represented for the system 300 of FIG. 3 is a reset button 314coupled to a reset node (SYS_CLR) of the safety fault interruptercircuit 102B to reset fault monitoring operations as desired. The safetyfault interrupter circuit 102B also includes an alarm node that couplesto a light-emitting diode (LED) and/or other messaging components tobroadcast when the safety fault interrupter circuit 102B is notoperating correctly.

FIG. 4 shows a schematic diagram of a safety fault monitoring scenario400, where various internal components of a safety fault interruptercircuit 102C are represented in accordance with various examples. InFIG. 4, the safety fault interrupter circuit 102C is an example of thesafety fault interrupter circuit 102 of FIG. 1, the safety faultinterrupter circuit 102A of FIG. 2, or the safety fault interruptercircuit 102B of FIG. 3). In some examples, the safety fault interruptercircuit 102C has a safety fault monitor (now shown) configured to detectground faults. In other examples, the safety fault interrupter circuit102C has a safety fault monitor (not shown) configured to detect arcfaults.

As represented in FIG. 4, the safety fault interrupter circuit 102Cincludes a resistive load 412 and shunt regulator 414 coupled betweenthe resistive load 412 and a ground node. The shunt regulator 414provides internal voltage regulation to the internal circuitryrepresented by resistive load 412, which represents fault monitorcomponents (e.g., components of the safety fault monitor 112 in FIG. 1)that operate using BIAS_1. In one example, the voltage sensing describedearlier in FIG. 2, the safety fault interrupter circuit 102C performsthe operations described for safety fault interrupter circuit 102A,where V_FB and V_REF are used to identify a current fault or wiringfault, and where switching operations related to the resistive load 412are powered by BIAS_1 to assert a fault interrupter signal in responseto a trigger (e.g., a current fault or a wiring fault).

In FIG. 4, BIAS_1 is provided to the safety fault interrupter circuit102C via two resistors, RD_1 and RD_2 (an example of R_DROP1 in FIG. 2and R_DROP2 in FIG. 3), and a capacitor, C_IN1 (an example of C2 in FIG.2, or C4 in FIG. 3). RD_1 and RD_2 are redundant resistor elements inorder to meet respective safety requirements, which demand a safecondition after a single component failure (in this case a shorted oropen circuit component). In the example of FIG. 4, RD1, RD2, and C_IN1are components of a power converter (e.g., the first power converter 114in FIG. 1) to provide BIAS_1 to the safety fault interrupter circuit102C. In some examples, safety fault monitor components represented bythe resistive load 412 use BIAS_1 for ground fault detection (e.g.,electrocution and/or wiring fault detection), and for switchingoperations such that a detected fault results in a switch 408 (labeled“SW1”) being closed to assert a fault interrupter signal. In otherexamples, the safety fault monitor components represented by theresistive load 412 use BIAS_1 for arc fault detection.

The safety fault interrupter circuit 102C also includes a voltage sensecircuit 402 (an example of the voltage sense circuit 110 in FIG. 1)coupled to a driver circuit 404 (an example of the driver circuit 106 inFIG. 1), where the driver circuit 404 uses BIAS_2 to selectively operatea switch 410 (labeled “SW2”) based on comparison results determined bythe voltage sense circuit 402. In FIG. 4, BIAS_2 is provided to thesafety fault interrupter circuit 102C via R_AUX3 (an example of R_AUX1in FIG. 2 and R_AUX2 in FIG. 3) and a capacitor, C_AUX1 (an example ofC3 in FIG. 2, or C5 in FIG. 3). In the example of FIG. 4, R_AUX3 andC_AUX1 are part of a power converter (e.g., the second power converter116 in FIG. 1) to provide BIAS_2 to the safety fault interrupter circuit102C.

In at least some examples, a shunt regulator 416 is placed between theBIAS_2 input of the driver circuit 404 and a ground node to providededicated voltage regulation to the circuitry used to detect a primaryor BIAS_1 power fault condition, and to operate the voltage sensecircuit 402, the driver circuitry 404, and the switch 410 to de-energizea load when a primary or BIAS_1 power fault occurs (e.g., if RD_1 orRD_2 fail in an open circuit condition). In the example of FIG. 4, thevoltage sensor circuit 402, the driver circuit 404, and switch 410correspond to a power fault monitor (e.g., the power fault monitor 104of FIG. 1, the power fault monitor 104A of FIG. 2, or the power faultmonitor 104B of FIG. 3) for the safety fault interrupter circuit 102C,where BIAS_2 provides power to the voltage sense circuit 402, the drivercircuitry 404, and the switch 410 to assert a fault interrupter signalin response to a trigger (e.g., a primary or BIAS_1 power fault)

In some examples, the driver circuit 404 causes the switch 410 to close(asserting a fault interrupter signal, such as an SCR signal) when thecomparison result indicates that a drop rate of BIAS_1 relative to adrop rate of BIAS_2 voltage exceeds a predetermined threshold. Indifferent examples, the threshold varies depending on the specificimplementation for a given IC and associated external circuitry. In someexamples, the driver circuit 404 causes the switch 410 to close(asserting a fault interrupter signal, such as an SCR signal) when thecomparison result indicates that the difference between BIAS_1 andBIAS_2 is more than a threshold amount or BIAS_1 changes relative toBIAS_2 at a rate greater than a threshold.

In FIG. 4, blocks 406A and 406B (labeled “I_LIMIT and SIG CON”) are usedto control and condition the power signals used to trigger respectiveactuators for de-energizing power to a load. In one example (see FIG.2), the trigger signal described as SCR is used to trip an SCR switch(Q1), which result in a low impedance across bridge rectifier 216 andengagement of the solenoid 214 to open the latching contacts 212.

In an example scenario, the resistive load 412 represents ground fault(e.g., electrocution and/or mis-wiring fault) monitoring componentswithin the IC. In another example scenario, the resistive load 412represents arc fault monitoring components within the IC. In someexamples, the resistive load 412 needs up to 20 mW to properly power theassociated internal circuitry with an example minimum voltagerequirement of 6V. In some examples, the internal shunt regulator 414 isset to 12V, depending on the specific IC implementation. In thisexample, the necessary current passing through the resistive load 412 iscalculated as 6V/0.02 W=3 mA. Also, the resistive load 412, representinga safety fault monitor, is calculated with R=P/I²=2.2 kΩ.

To support a safety fault interrupter circuit 102C for the above-notedpower specifications, the values for RD_1 and RD_2 are selected tosupply a minimum input voltage of 6V. If, as an example, 90 VDC isassumed as the minimum, the combined value for RD_1 and RD_2 is (90VDC−6 VDC)/3.0 mA=28 kΩ. In one example, RD_1 and RD_2 are selected tohave a combined value of approximately 28 kΩ (e.g., RD_1=RD_2=13.5 kΩ,where rounding down by 1 kΩ total (500 ohm each) in order to accommodatecomponent tolerance. Now sizing RD_1 and RD_2 for an overvoltagescenario (e.g., 240 VAC), a value of (339V−12V)/27K=12.1 mA. In thisexample the losses for RD_1 and RD_2 are approximated to be 1.98 Wattseach. Accordingly, RD_1 and RD_2 are sized as 2 W components. AssumingBIAS_2 load circuitry 404, 406B, 410 requires 150 uA to operateproperly, and a minimum of 90 VAC for this example scenario, an R_AUX3value of 760 kΩ is appropriate (with a loss of 148 mW during a 240 VACovervoltage scenario), where R_AUX3 is implemented as a 0402 or 0603size resistor. Also for this example scenario, a no power-fault examplemagnitude for BIAS_1 is 6V, and an example no power-fault magnitude forBIAS_2 is 6V, where timing/storage capacitors, C_IN1 and C_AUX1, arechosen to ensure the circuitry powered by BIAS_2 maintains properoperation after the magnitude of BIAS_1 is below a predeterminedthreshold. As an example, BIAS_2 should allow proper operation of thedriver 404 and the switch 410 to create the trigger signal used toeventually de-energize the load. In other examples, the componentvalues, the BIAS_1 value, and the BIAS_2 vary from the example valuesgiven. Such variance could be due to supporting different safety faultdetection options and power fault monitor options as described herein.

Regardless of the particular faults being supported by BIAS_1, the lowpower circuitry associated with BIAS_2 enables BIAS_1 to be monitored.The circuitry needed to monitor BIAS_1 has low power consumption andthus requires little current. Thus, in some examples, resistors withsmall size, low-cost, and high-resistance are used for the auxiliaryresistance (e.g., R_AUX1-R_AUX5 in FIGS. 2-5B) that enables monitoringof BIAS_1 in contrast to the drop resistors used to provide BIAS_1(e.g., R_DROP1 in FIG. 2, R_DROP2 in FIG. 3, and RD_1 and RD_2 in FIG.4). In some examples, using a power fault monitor as described herein(e.g., the power fault monitor 104 in FIG. 1, the power fault monitor104A in FIG. 2A, the power fault monitor 104B in FIG. 3, or respectivecomponents in FIG. 4) enables the number of drop resistors used toprovide BIAS_1 to be reduced from four to two, which significantlyreduces the footprint and power consumption of components needed tosupport an IC with a safety fault monitor as described herein (e.g., thesafety fault monitor 112 in FIG. 1, the safety fault monitor 112A inFIG. 2A, the safety fault monitor 112 in FIG. 3, or respectivecomponents in FIG. 4).

FIG. 5A shows a schematic diagram of a safety fault monitoring scenario500, where various internal components of the safety fault interruptercircuit 102C are represented in accordance with various examples. In thefault monitoring scenario 500, the same safety fault interrupter circuit102C represented in FIG. 4 is presented. The difference between thesafety fault monitoring scenario 400 of FIG. 4 and the safety faultmonitoring scenario 500 of FIG. 5 is that an SMPS 502 is used to provideBIAS_1. In some examples, a capacitor, C_IN2, couples between aninput-side of the SMPS 502 and a ground node. In addition, anothercapacitor, C_O1, couples between an output-side of the SMPS 502 and aground node (e.g., C_O1 couples between a BIAS_1 node 506 of the safetyfault interrupter circuit 102C and a ground node). As represented inFIG. 5A, in addition to providing BIAS_1 to the safety fault interruptercircuit 102C, the SMPS 502 also supports optional circuitry 504, such asmicroprocessors, voltage/current monitors, wireless communicationcomponents, and/or other components to support “smart” fault monitoringand interrupt operations.

For scenario 500, the operations of the safety fault interrupter circuit102C of FIG. 5A follow the discussion provided for the scenario 400 ofFIG. 4, where BIAS_1 is provided by the SMPS 502. As desired, the valuesfor RD1, RD2, C_IN1, C_AUX1, and R_AUX1 in FIG. 4 are selected tosupport particular power consumption values and/or no power-faultmagnitudes for BIAS_1 and BIAS_2 and/or to support other operations(e.g., how quickly BIAS_1 and BIAS_2 change in response to brown-outs,black-outs, and/or other fault conditions). Similarly, the values forC_O1, C_IN2, R_AUX4, C_AUX2 in FIG. 5A are selected to supportparticular power consumption values, particular no power-faultmagnitudes for BIAS_1 and BIAS_2, and/or to other operations (e.g., howquickly BIAS_1 and BIAS_2 change in response to brown-outs, black-outs,and/or other power fault conditions).

FIG. 5B shows a schematic diagram of another safety fault monitoringscenario 520, where various internal components of a safety faultinterrupter circuit 102D are represented in accordance with variousexamples. In the fault monitoring scenario 520, the safety faultinterrupter circuit 102D is the same as the safety fault interruptercircuit 102C represented in FIGS. 4 and 5A, except that the safety faultinterrupter circuit 102D includes analog-to-digital converter (ADC) andinterface block 506. The ADC/interface block 506 enables the safetyfault interrupter circuit 102D to communicate with the optionalcircuitry 504 introduced in FIG. 5A to support “smart” fault monitoringand interrupt operations. In at least some examples, BIAS_2 powers theADC/interface block 506 as represented in FIG. 5B.

In some examples, the various components external to the safety faultinterrupter circuit 102D (e.g., C_O2, C_IN3, R_AUX5, C_AUX3) in scenario520 are the same components introduced in scenario 500 (e.g., C_O2=C_O1,C_IN3=C_IN2, R_AUX5=R_AUX4, C_AUX3=C_AUX2). In other examples, thevalues for the external component in FIGS. 5A and 5B are adjusted toaccount for the ADC/interface 506, the optional circuitry 504, and/orother system components.

The safety fault interrupter circuits described herein (e.g., the safetyfault interrupter circuit 102 in FIG. 1, the safety fault interruptercircuit 102A in FIG. 2, the safety fault interrupter circuit 102B inFIG. 3, the safety fault interrupter circuit 102C in FIGS. 4 and 5A, andthe safety fault interrupter circuit 102D in FIG. 5B) provide thebenefit of reducing the overall footprint and cost of components neededto support IC biasing. This is because there are low currentrequirements for BIAS_2 in order to perform the voltage sensingoperations (see e.g., the description for the voltage sensing circuit110 in FIG. 1) and to trigger a dedicated fault circuit when a powerfault condition is identified. In one example, the use of largeresistors needed to support an existing safety fault interrupter circuitwith a single biasing node, is reduced from four resistors (at least 2 Weach) to two resistors (less than 2 W each). While an additional small0402/0602 resistor (one of R_AUX1-R_AUX5) and capacitor (one of C3, C5,or C_AUX1-C_AUX3) is used, the overall footprint of external componentsto support BIAS_1 and BIAS_2 is reduced compared to an existing safetyfault interrupter circuit with a single bias node. In addition, faultmonitoring based on BIAS_2 enables early power loss indication andtriggering of a fault interrupter signal (e.g., an SCR signal) todisconnect an AC load based on a new fault condition.

For scenarios involving SMPS, fault monitoring based on BIAS_2 is usedto identify when the SMPS stage has failed and to respond byde-energizing the AC load before power is totally lost. As desired, insome examples, the early indication of an SMPS fault and/or power lossis used by optional circuitry (e.g., circuitry 504 in FIGS. 5A and 5B)to notify host elements (e.g., a network or user) of an imminent faultcondition. In this example, the ADC/interface block 506 digitizessignals as needed and uses bus standards (e.g., I2C or SPI) tocommunicate with microcontrollers and/or microprocessors performing“smart” fault monitoring and response operations.

Certain terms have been used throughout this description and claims torefer to particular system components. As one skilled in the art willappreciate, different parties may refer to a component by differentnames. This document does not intend to distinguish between componentsthat differ in name but not function. In this disclosure and claims, theterms “including” and “comprising” are used in an open-ended fashion,and thus should be interpreted to mean “including, but not limited to .. . .” Also, the term “couple” or “couples” is intended to mean eitheran indirect or direct wired or wireless connection. Thus, if a firstdevice couples to a second device, that connection may be through adirect connection or through an indirect connection via other devicesand connections. The recitation “based on” is intended to mean “based atleast in part on.” Therefore, if X is based on Y, X may be a function ofY and any number of other factors.

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present invention. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the followingclaims be interpreted to embrace all such variations and modifications.

What is claimed is:
 1. An apparatus that comprises: a safety faultinterrupter circuit, wherein the safety fault interrupter circuitcomprises: a safety fault monitor coupled to a first bias node andconfigured to selectively assert a fault interrupter signal based atleast in part on a first bias voltage and a first power consumption; anda power fault monitor for the safety fault monitor, wherein the powerfault monitor is coupled to a second bias node and configured toselectively assert the fault interrupter signal based at least in parton a second bias voltage and a second power consumption, wherein thesecond power consumption is less than the first power consumption. 2.The apparatus of claim 1, wherein the power fault monitor comprises avoltage sense circuit configured to compare the first bias voltage andthe second bias voltage, and to determine a comparison result, andwherein the power fault monitor is configured to selectively assert thefault interrupter signal based on the comparison result.
 3. Theapparatus of claim 2, wherein the fault interrupter signal is assertedby the power fault monitor when the comparison result indicates that adrop rate of the first bias voltage relative to a drop rate of thesecond bias voltage exceeds a threshold.
 4. The apparatus of claim 2,wherein the fault interrupter signal is asserted by the power faultmonitor when the comparison result indicates that the difference betweenthe first and second bias voltages is greater than a threshold amount.5. The apparatus of claim 2, wherein the power fault monitor furthercomprises: a driver circuit coupled to the voltage sense circuit; and aswitch coupled to the driver circuit, wherein the driver circuit isconfigured to assert a control signal to the switch based on thecomparison result, wherein the switch is configured to allow currentflow in response to an asserted control signal from the driver circuit,and wherein the current flow results in the fault interrupter signal. 6.The apparatus of claim 1, wherein the safety fault interrupter circuitfurther comprises: a first voltage regulator coupled between the firstbias node and a ground node; and a second voltage regulator coupledbetween the second bias node and a ground node.
 7. The apparatus ofclaim 1, where the first bias node is configured to receive the firstbias voltage from a diode rectifier followed by a resistor-capacitor(RC) or a switched-mode power supply (SMPS), where the second bias nodeis configured to receive the second bias voltage via aresistor-capacitor (RC) circuit coupled to an input side of the SMPS. 8.The apparatus of claim 1, where the first bias node is configured toreceive the first bias voltage via a resistor-capacitor (RC) circuit,wherein the RC circuit is a first RC circuit, and wherein the secondbias node is configured to receive the second bias voltage via a secondRC circuit coupled to an input side of the first RC circuit, wherein thesecond RC circuit has a higher resistance than the first RC circuit. 9.The apparatus of claim 1, wherein the safety fault monitor is configuredto detect ground faults.
 10. The apparatus of claim 1, wherein safetyfault monitor is configured to detect arc faults.
 11. The apparatus ofclaim 1, further comprising an analog-to-digital signal converter (ADC)configured to convert one or more analog signals determined by the faultinterrupter circuit into digital signals for use by a microprocessor.12. The apparatus of claim 1, wherein the safety fault interruptercircuit is a ground fault circuit interrupter (GFCI), and the faultinterrupter signal is a silicon-controlled rectifier (SCR) signal.
 13. Asafety fault interrupter integrated circuit (IC) that comprises: asafety fault monitor circuit configured to selectively assert a faultinterrupter signal; and a power fault monitor circuit for the safetyfault monitor circuit, wherein the power fault monitor circuit isconfigured to selectively assert the fault interrupter signal, andwherein the power fault monitor circuit comprises: a voltage sensecircuit configured to compare a first voltage input to the safety faultmonitor circuit and a second voltage input to the power fault monitorcircuit, and to determine a comparison result; and a switch operatedbased on the comparison result.
 14. The safety fault interrupter IC ofclaim 13, wherein the first voltage is a first bias voltage input to thesafety fault monitor circuit, wherein the second voltage is a secondbias voltage input to the power fault monitor circuit, and wherein apower consumption of the power fault monitor circuit is less than apower consumption of the safety fault monitor circuit.
 15. The safetyfault interrupter IC of claim 13, wherein the power fault monitorcircuit further comprises a driver circuit coupled to the voltage sensorcircuit, wherein the driver circuit is configured to assert a controlsignal to the switch based on the comparison result, wherein the switchis configured to allow current flow in response to an asserted controlsignal from the driver circuit, and wherein the current flow results inthe fault interrupter signal.
 16. The safety fault interrupter IC ofclaim 12, further comprising: a first node coupled to the safety faultmonitor circuit; and a second node coupled to the power fault monitorcircuit, wherein the first node is configured to receive the firstvoltage from a switch-mode power supply (SMPS), and wherein the secondnode is configured to receive the second voltage via aresistor-capacitor (RC) circuit coupled to an input side of the SMPS.17. The safety fault interrupter IC of claim 12, further comprising: afirst node coupled to the safety fault monitor circuit; and a secondnode coupled to the power fault monitor circuit, wherein the first nodeis configured to receive the first voltage from a firstresistor-capacitor (RC) circuit, and wherein the second node isconfigured to receive the second voltage via a second RC circuit coupledto an input side of the first RC circuit.
 18. An integrated circuit (IC)that comprises: a first node configured to receive a first voltage; asecond node configured to receive a second voltage; a safety faultmonitor circuit configured to use the first voltage to power switchingoperations to assert a fault interrupter signal in response to a firsttrigger, wherein the safety fault monitor circuit has a first powerconsumption; and a power fault monitor circuit configured to use thesecond voltage to power switching operations to assert the faultinterrupter signal in response to a second trigger, wherein the powerfault monitor circuit has a second power consumption that is less thanthe first power consumption.
 19. The IC of claim 18, wherein the powerfault monitor circuit comprises: a voltage sense circuit configured toperform a comparison of the first voltage and the second voltage; atransistor-based switch; and a driver circuit, wherein the switchingoperations involve the driver circuit selectively asserting a drivesignal to a control terminal of the transistor-based switch in responseto the comparison indicating that a drop rate of the first voltagerelative to a drop rate of the second voltage exceeds a threshold. 20.The IC of claim 18, wherein the power fault monitor circuit comprises: avoltage sense circuit configured to perform the comparison of the firstvoltage and the second voltage; a transistor-based switch; and a drivercircuit, wherein the switching operations involve the driver circuitselectively asserting a drive signal to the control terminal of thetransistor-based switch in response to the comparison indicating thatthe difference between the first and second voltages is greater than athreshold amount.
 21. The IC of claim 18, wherein the second triggerindicates a power loss condition for the safety fault monitor circuit,and wherein the fault interrupter signal is a silicon-controlledrectifier (SCR) signal.